Knowledge Representation for the Semantic Web Winter Quarter 2011 Pascal Hitzler Slides 4 – 01/13/2010 Kno.e.sis Center Wright State University, Dayton, OH http://www.knoesis.org/pascal/ KR4SW – Winter 20 11 – Pascal Hitzler
Textbook (required) Pascal Hitzler, Markus Krötzsch, Sebastian Rudolph Foundations of Semantic Web Technologies Chapman & Hall/CRC, 2010 Choice Magazine Outstanding Academic Title 2010 (one out of seven in Information & Computer Science) http://www.semantic-web-book.org 2 KR4SW – Winter 20 11 – Pascal Hitzler
Today: RDF syntax – RDF Schema 3 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 4 KR4SW – Winter 20 11 – Pascal Hitzler
Motivation • RDF allows to express facts – Anne is the mother of Merula • But we’d like to be able to express more generic knowledge – Mothers are female – If somebody has a daughter then that person is a parent • This kind of knowledge is often called schema knowledge or terminological knowledge. • RDF Schema allows us to do some schema knowledge modeling. OWL (discussed later) gives even more expressivity. 5 KR4SW – Winter 20 11 – Pascal Hitzler
RDF Schema (RDFS) • part of the W3C Recommendation RDF • for schema/terminological knowledge • uses RDF vocabulary with pre-defined semantics • every RDFS document is an RDF document • Namespace: http://www.w3.org/2000/01/rdf-schema# - usually abbreviated by rdfs: • vocabulary is generic, not bound to a specific application area – allows to (partially) specify the semantics of other/user- defined vocabularies (it‘s a kind of meta vocabulary) – hence, RDF software correctly interprets each vocabulary defined using RDF Schema 6 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 7 KR4SW – Winter 20 11 – Pascal Hitzler
Classes and Instances • Classes stand for sets of things. In RDF: Sets of URIs. • book:uri is a member of the class ex:Textbook • a URI can belong to several classes • classes can be arranged in hierarchies: each textbook is a book 8 KR4SW – Winter 20 11 – Pascal Hitzler
Pre-defined classes • every URI denoting a class is a member of rdfs:Class • this also makes rdfs:Class a member of rdfs:Class (!) • rdfs:Resource (class of all URIs) • rdf:Property (class of all properties) • rdf:XMLLiteral • rdfs:Literal (each datatype is a subclass) • rdf:Bag, rdf:Alt, rdf:Seq, rdfs:Container , rdf:List, rdf:nil, rdfs:ContainerMembershipProperty (see later) • rdfs:Datatype (contains all datatypes – a class of classes) • rdf:Statement (see later) 9 KR4SW – Winter 20 11 – Pascal Hitzler
Implicit knowledge • if an RDFS document contains and then is implicitly also the case: it’s a logical consequence . (We can also say it is deduced (deduction) or inferred (inference). We do not have to state this explicitly. Which statements are logical consequences is governed by the formal semantics (covered in the next session). 10 KR4SW – Winter 20 11 – Pascal Hitzler
Implicit knowledge – another example • From the following is a logical consequence: I.e. rdfs:subClassOf is transitive . 11 KR4SW – Winter 20 11 – Pascal Hitzler
Using implicit knowledge Ontology (Knowledge Base) e.g. RDF or OWL online Used like a database Reasoner (accesses implicit knowledge) Application 12 KR4SW – Winter 20 11 – Pascal Hitzler
Using implicit knowledge Ontology (Knowledge Base) e.g. RDF or OWL Used like a Reasoner (produces implicit knowledge) database offline Completed (materialized) knowledge base Application 13 KR4SW – Winter 20 11 – Pascal Hitzler
Class equivalence I.e. rdfs:subClassOf is reflexive . 14 KR4SW – Winter 20 11 – Pascal Hitzler
Classes and RDF/XML syntax is short for 15 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 16 KR4SW – Winter 20 11 – Pascal Hitzler
Property Hierarchies From and we can infer that 17 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 18 KR4SW – Winter 20 11 – Pascal Hitzler
Property Restrictions • Allow to state that a certain property can only be between things of a certain rdf:type. • E.g. when a is married to b, then both a and b are Persons. • Expressed by rdfs:domain and rdfs:range: • And similarly for datatypes: 19 KR4SW – Winter 20 11 – Pascal Hitzler
Pitfalls 1 states that everything in the rdfs:range of ex:authorOf is both a ex:Textbook and a ex:Storybook! 20 KR4SW – Winter 20 11 – Pascal Hitzler
Pitfalls 2 A logical consequence of this is 21 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 22 KR4SW – Winter 20 11 – Pascal Hitzler
Open Lists revisited • New class: rdfs:Container as superclass of rdf:Seq, rdf:Bag, rdf:Alt. • New class: rdfs:ContainerMembershipProperty containing the properties used with containers, e.g. 23 KR4SW – Winter 20 11 – Pascal Hitzler
Open Lists revisited • New property rdfs:member Is superproperty of all properties contained in rdfs:ContainerMembershipProperty. • The RDFS semantics specifies: From and the following is inferred: 24 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 25 KR4SW – Winter 20 11 – Pascal Hitzler
Talking about triples • How do you state in RDF: “The detective supposes that the butler killed the gardener.” • unsatisfactory: • We would really like to talk about the triple 26 KR4SW – Winter 20 11 – Pascal Hitzler
Talking about triples • How to do it properly in RDFS: • Note however, that the following is not a logical consequence of this: • One would usually use a blank node instead of ex:theory. 27 KR4SW – Winter 20 11 – Pascal Hitzler
A reification puzzle You know that story? It’s in the old testament :) 28 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 29 KR4SW – Winter 20 11 – Pascal Hitzler
Supplementary information • comments etc. which are not part of the actual ontology, but are for the human reader/user/developer • in RDF, we also use triples to encode these • i.e. we have a set of pre-defined properties which do this job • rdfs:label: e.g. to give a human-readable name for a URI • rdfs:comment: used for lengthy commentary/explanatory text • rdfs:seeAlso, rdfs:definedBy: properties pointing to URIs where further information or definitions can be found 30 KR4SW – Winter 20 11 – Pascal Hitzler
Supplementary Information example 31 KR4SW – Winter 20 11 – Pascal Hitzler
Today’s Session: RDF Schema 1. Motivation 2. Classes and Class Hierarchies 3. Properties and Property Hierarchies 4. Property Restrictions 5. Open Lists Revisited 6. Reification 7. Supplementary Information in RDFS 8. Simple Ontologies in RDFS 9. Class project 10. Class presentations 32 KR4SW – Winter 20 11 – Pascal Hitzler
An example ontology 33 KR4SW – Winter 20 11 – Pascal Hitzler
The same as graph 34 KR4SW – Winter 20 11 – Pascal Hitzler
Note the multiple views: XML 35 KR4SW – Winter 20 11 – Pascal Hitzler
Note the multiple views: RDF 36 KR4SW – Winter 20 11 – Pascal Hitzler
Note the multiple views: RDF Schema 37 KR4SW – Winter 20 11 – Pascal Hitzler
Recommend
More recommend
